Ford C4 Transmission Swap

Installing a Ford C4 transmission into a Merkur XR4Ti powered by Ford 2.3 turbo engine.

THE PROBLEM....

Stock Merkur XR4Ti 5sp with "toothless" 2nd gear

The stock Merkur 5 speed transmission (known as the T9) is far from being a pillar of strength.  I got my Merkur XR4Ti with 54K miles several years ago.  I babied the T9 transmission for many years.  As I modified the car over the years, I kept expecting the transmission to go out.  I avoided stuff like burn outs, speed shifting, anything that abused the transmission... overall, I shifted it like a grandma.  After years past with no noise, no signs of wear, no problems (other than the typical crummy T9 shifter - a factory "feature"), I was beginning to think that the thing might outlast the car... or me.

Then, last Summer as I was driving to work one morning, it finally happened. I got onto the freeway on ramp and was slowly accelerating. I gently shifted to 2nd and gradually put my foot into it (shifting like a grandma again). Acceleration was brisk.  Then boost peaked and I got the usually kick in the pants - like when hitting a power band.  Right after boost peaked and the car began accelerating hard, there was a very loud "BANG" and my hand (still on the shifter - anticipating a shift to 3rd) could feel the disaster below. As I coasted to the shoulder, the car was lurching as the drive line was locking up.  As it turns out, all the teeth were ripped off of 2nd gear.
 

THE SOLUTION....

"Bullet Proof" C4 Transmission and Torque Converter

It would have been easy enough to just get another stock Merkur XR4Ti transmission and quickly swap it in.  I even have a Merkur parts car which has what appears to be a good, stock 5 speed transmission.  That would have only been a temporary fix.  I wasn't interested in getting stranded on the side of the road again.  Besides, it was no fun having to baby the old transmission all those years.  It's nice to be able to drive a car and not worry about things breaking all the time.  So, I decided that it was time to upgrade to something more suitable for the car.  I'd like to do some "family" drag racing (not running the 1/4 mile with the whole family in the car!).... just going out to the track with the family and doing some recreational racing.  I know that my 2 boys would LOVE it!  They are natural car nuts (they prefer Matchbox cars right now) and the sights and sounds of the drag strip would be a lot of fun for them.  Then there's my daughter, Rachel Leigh (nearly 5 yrs.old).... I know exactly what she'd say.... "Hmmmmm, I don't like this.  It's too handsome."   That's her way of saying, I don't like this "boy stuff", and I would rather be playing with my dolls.

Anyway, wanting the car to be able to stand up to drag racing (as well as reliably serve as my daily driver), I decided to pursue transplanting in something strong... something that was intended for a high performance V8.  The natural choice was a Ford C4 automatic transmission.  I began researching sources for a C4.  As usual, I was looking for the best "bang for the buck".  I didn't wanted a stock Ford C4 transmission - which probably would have been just fine since Ford put them behind millions of V8 engines over the years.  But, I wanted to get a high performance built C4 so that it would be able to survive in the Merkur over the long term.  By the way, the Merkur never came from the factory with a C4.   Automatic equipped Merkurs were given the weak C3 transmission.  I definitely was not interested in putting one of those in the car - although it would have been a much simpler, bolt in installation!  The C4 install required a fair amount of custom work.  It's not something to be tackled by someone who doesn't have an interest in spending a fair amount of time working on their car and doing (or having someone else do) some custom fabrication.  Of all the projects I've done on my Merkur, I'd say that this C4 transmission swap involved the most details.  I spent several long Saturdays working on this.  Many of those Saturdays were 12+ hour work days.  The last Saturday, I was out there for around 24 hours getting the swap completed.  It is a fair amount of work to gather all the necessary parts and make it all work properly.

Here's an important side note.... the best way to get a C4 transmission to bolt to a Ford 2.3 engine is to find a special bell housing which Ford put on a very limited number of cars in the 70's.  It's possible to use a C4 bell housing from a 2.0 engine car, but that requires some special stepped dowel pins.  Not a big deal.  But, the easiest choice is the C4/2.3 bell housing (D42F 7976 AA).  It's possible to find these old bell housings, but they are not lying around in every junkyard.  They are not easy to find.  Because of their limited numbers and the demand for these, I've seen them selling on Ebay for $200-$300!  You can get more common C4 bell housings for around $20.  It's good old "supply and demand" at work.  Anyway, I searched quite a while before running across one of these.  In fact, I got mine in an unexpected way.

I was calling around locally looking for a Ford C4 transmission core that could be built up (just the transmission - not the bell housing).  As it turns out, I was talking to a small auto repair shop just a few miles from where I work.  I asked if they had an old C4 core they wanted to get rid of.  The guys said he thought that they did have one laying out back... he thought it was from an old Pinto.  I figured it was just the transmission itself (which was all I was looking for at the time).  I went over there and when the guy took me out back, I saw an old C4 sitting in the dirt and weeds.  Looked like it had been sitting there for many years.  I was surprised to see that the bell housing was still on the transmission.  I was even more surprised when I saw the Ford casting number.... it was one of the rare 2.3/C4 bell housings!!  There were millions of C4's made and put into V6 and V8 cars over the years, but the Ford C4 in a Pinto with a 2.3L 4 cylinder engine is the rare gem to find.  When I asked the guy how much he wanted for it, he said something like "O, you can have it for $15".  OK!  Needless to say, I was blessed to get the C4/2.3 bell housing and a C4 core for only $15.  One man's junk is another man's treasure!

Enough about the bell housing.... back to the transmission... after much research I decided to order an Accurate Transmission "Bullet Proof" C4 through the local Advance Auto Parts store.  After researching extensively, I was very comfortable with Accurate's capabilities.  They are a very big transmission remanufacturer, have state of the art equipment, trained staff, and LOTS of experience.  They remanufacture an unbelievable number of transmissions every year.  They are the source for remanufactured transmissions for 3 O.E.M. auto makers.  They are supposed to have over 5000 remanufactured transmissions in stock and ready to ship.  Their Bullet Proof series was designed for heavy duty applications.  The C4 transmission was built up with high performance clutch materials, extra clutch discs in the pack, a modified valve body for firmer shifts, and also supposed to have increased oil flow.  The transmission came with a high performance torque converter with a slightly higher than stock stall speed (plus 300-400rpm) and reinforcements in key areas.  With a special going on at the local Advance Auto Parts store, I got the Bullet Proof C4 transmission and torque converter for around $650.  Not bad... considering all the features and also because the Bullet Proof series comes with a 18 month, unlimited miles warranty.

"Bullet Proof" C4 Torque Converter

One thing that I didn't like about the Accurate built C4 was the fact that the shift lever came installed upside down - at least it was the wrong way for my application.  The instructions say that the shift lever must be repositioned depending on the car.  This makes sense, but I wasn't expecting to have to pull the valve body out and mess with the shift lever.  Fortunately, it didn't take too long.  I rotated the shift arm 180 degrees, got the valve body back in, carefully re-torqued it, and was soon back to working on getting the transmission in the car.

Valve Body Out for Repositioning Shift Arm

Early on in the planning stages of the project, I decided that I wanted to get a transmission oil pan that had a drain plug.  I don't care for having to loosen the whole pan for service, and then taking a bath in transmission fluid as it spills all over the place.  I picked up a cheap after market C4 oil pan with drain plug through Ebay.  As a added bonus, the pan was slightly deeper (appears to have an extra quart of fluid capacity).

After Market C4 Oil Pan

Since my car was originally equipped with a 5 speed, I needed to get some stuff to convert it over to a automatic.  I got most of the Merkur Auto parts that I needed from a nice guy on one of the Lists I am a part of on-line.  For the rest of the stuff I needed, once again I shopped around on the internet.   I found a great source for new automatic transmission parts - Makco Distributing.  They have a great selection, great prices, and very good service.  One of the things that I got from them was a green stripe vacuum modulator that is designed to be able to handle turbo boost.  I also bought a C4 flex plate (aka. automatic flywheel).  They also carry a full line of high performance automatic transmission parts.

C4/2.3 Flex Plate Installed

As a side note to the flex plate... I had some frustration trying to pull the old clutch pilot bearing out of the back of the crankshaft.  The roller bearing was pressed in there good!  After a couple trips to town looking for tools, I finally came back with a slide hammer and attachments.  After shredding the bearing (only the shell was left in the crank), I finally got it out.  Beware - those of you that buy from Harbor Freight Tools - the pilot bearing puller tool they sell did not work for me.  According to the specs on the box it should work, but as is typical of some "Made In China" tools, there can be a huge variation in quality from piece to piece.  The puller jaws came no where close to fitting inside the pilot bearing.  The smallest diameter they adjusted down to was around 3/4".  Package said they would adjust down to 1/2".  I went back to Harbor Freight and measured several of the pullers on the shelf.  They all varied a lot, but none of them would go down to 1/2".  The moral of the story is:  make sure your pilot bearing puller will fit before you leave the store.  I have heard that some people have used this Harbor Freight puller successfully, but they must have purchased one from a different batch - where the tool was actually made to spec.  Anyway, I finally bought the slide hammer kit with adapters and got the remains of the pilot bearing out.

After securing the flex plate, I then needed to get the C4 assembly up in place.  I had a transmission jack adapter, but unfortunately the car was not up high enough for me to be able to put the C4 on the stand and then just roll it under the car.  I needed to slide the C4 under the car, crawl under there, lay on my back, drag the C4 up on my chest, use my feet to pull the jack towards me, and then lift & push the C4 up onto the transmission adapter.  This maneuver was a chiropractor's dream!!  Obviously, with the transmission tunnel there's extra "head room", so the C4 could sit on top of the jack trans adapter and still have room under the car.  Once on the jack, the trans adapter worked real well in fine tuning the position of the Ford C4 transmission so I could bolt the bell housing to the engine.  Ideally, the car should be up higher so the transmission can placed on the jack and easily rolled under the car.  Thankfully, it was even possible to do what I did alone, because bench pressing a Ford C4 with one hand while trying to position and install the bolts is something best left to Arnold Schwarzenegger!

C4 Transmission Bolted to Engine

After bolting the bell housing to the engine, I then secured the torque converter to the flex plate with the necessary 4 nuts.  For critical fastener applications like these torque converter nuts, flex plate-crankshaft bolts, etc... I liberally used thread locker (Loc-Tite).  I didn't want any of these critical fasteners to come loose!

Another decision I made in my transplant was to try and use the stock Merkur XR4Ti automatic shifter.  In order to do this, the shifter arm on the C4 transmission needs to be the same length as on a stock Merkur C3 transmission arm.  Some C4's might have the same length (approx. 2.5" from shaft center to linkage pivot point), but the arm on the Ford C4 I got was too short.  I decided to make a simple adapter out of some 1/8" thick steel flat stock.  I took some quick measurements and cut a section of flat stock.  I then drilled a couple appropriately size holes in it and bolted the adapter to the C4 shifter arm.  I tightened this bolt enough so that it wouldn't easily slip.  I used a smaller bolt up top that would fit through the pivot end of the Merkur shift linkage rod.  I used a longer bolt so that there would be a smooth shoulder that contacted the linkage pivot bushing, and just cut off the extra threads that I didn't need.   After adjusting the position of the adapter so that the shifter in the car matched the detents in the transmission, I permanently secured the adapter arm by welding it to the C4 shifter arm along one side.   In the picture below, you can see the simple adapter arm and linkage rod attached.  By the way, I decided that I didn't want to install a kick down linkage yet, so I used a couple washers as spacers and then secured this in place with a short section of fuel hose and a small clamp.  One thing I do not like about automatic transmissions is the way they will sometimes downshift at a time when you would rather have loaded down the engine in a higher gear.  So, I decided that I would try and run the car without the kick down lever/cable attached and see how it worked.  I might hook up the kick down cable in the future.

C4 Shift Arm Adapter with Linkage Rod Attached

Now here's an area the turned out different than I expected.... I was planning to use a stock Merkur Auto shifter assembly in the car and use the stock Auto shifter bezel (the plastic piece that fits around the shifter).  Well, I did do this, but it wasn't the way I had originally planned.  Here's why... When I was working on the shift arm adapter, I had installed the Auto Merkur XR4Ti shifter assembly in the car and set everything up so that the shifter worked right.  I then welded the adapter arm in place.  Later, I tried to install the plastic shifter bezel piece around the shifter.  It wouldn't fit.  Then I realized that even though the 5 speed shifter has the same mounting hole pattern as the Auto shifter, they are located in different positions.  In other words, the 5 speed and Auto shifters bolt to the car in different positions.  Had I realized this earlier, I would have drilled out some rivets that secured a mounting bracket to the car and move this to a new position.  This would have moved the Auto shifter to the proper location.  Since I already welded my adapter arm in place, and because I wasn't in the mood of trying to cut the shift linkage rod and then cut new threads on the rod end, I decided to try something different.  I used the 5 speed shifter bezel AND an Auto bezel "spliced" together.  I had an Auto shifter bezel that was cracked up pretty bad, and so I cut the bad section off and used part of it to cover the opening in the 5 speed bezel.  I won't go into all the details of how I spliced the 2 together, but it worked fine.  Obviously, I would have done this differently had I been aware of the different 5 speed and Auto shifter mounting positions.  I still have a good Auto shifter bezel, so I might re-do this in the future like it was done from the factory.  The following 2 pictures show the final shifter assembly inside the car and the piece of Auto bezel that I used to "splice" to the 5 speed bezel.  It looks OK and works just fine.
 

Merkur XR4Ti Auto Shifter with Spliced Bezel
 

Section of Auto Shifter Bezel Used

The next thing that needed to be worked out was the transmission cross member and mount.  I bought a couple different rubber Ford C4 transmission mounts, but as I lay under the car thinking about how I could make these work, I came to the conclusion that I would be better off trying to use the stock 5 speed T9 transmission mount and cross member.... if possible.  One morning I woke up and an idea hit me.  I took some measurements, got some angle iron, and came up with a simple adapter that allowed me to bolt the C4 transmission to the stock T9 trans mount - while still using the T9 cross member.  As a side note here... there are other ways of doing this.  It is possible to buy a custom fabricated C4 transmission cross member.  I just decided to do it this way, because it was a relatively simple idea that I thought would work.  It ended up working great.

Below are some pictures showing the adapter that I welded up from some angle iron.  You may notice a smaller hole next to one of the bigger mounting holes.  That's just proof of "recycling".  I used a section of old angle iron that I had in my scrap bin.  It had been pre-drilled for use in another application.  I like to dig through my collection of scrap materials and find just the right piece for a project.  It sure beats having to run to town to buy some new material.  Below are 3 pictures showing the adapter right after welding with my "spatter gun" (aka. flux core wire feed welder)... then a picture of the adapter attached to the T9 mount after painting with "cold galvanizing" paint... and finally a picture of the adapter/mount/crossmember installed in the car.

C4 Transmission Mount Adapter (no paint)
 

Adapter Painted and Attached to T9 Trans Mount
 

Final install of Ford C4 Transmission Adapter

One more comment on the transmission mount before moving on to the next topic... setting the driveshaft angle is VERY important in order to get a vibration free installation.  If the angles are not right, the drive line can vibrate bad - especially if you use a 1 piece drive shaft like I planned to do... more on that later.  I used a simple Harbor Freight magnetic protractor to measure the angle of the differential flange.  It was about 2.5 degrees.  I then shimmed (with washers) the transmission cross member down until I got a reading of 2.5 degrees off the end of the C4 output shaft.  This time, the 2.5 degrees needed to be in the other direction.  In other words, the centerline of the transmission output shaft must be set so that it is parallel to the centerline of the differential input shaft.

Speaking of driveshafts... that's the next piece of the C4 puzzle I will touch upon...

Since the Ford C4 transmission never came in the Merkur XR4Ti, it is necessary to come up with a custom driveshaft.  It is possible to try and modify a stock Merkur drive shaft with a C4 slip yoke and u-joint up front, but the last thing I wanted to do was spend all this time, effort, and money and have the skinny stock driveshaft with unserviceable u-joints be the weak link.  The stock Merkur comes from the factory with a 2 piece driveshaft.  There is a joint in the middle of the shaft and the shaft is secured by a center support bearing.  Apparently, this rather complex 2 piece design was implemented to deal with vibration inherent in this 4 cylinder application.  Switching to a simpler 1 piece shaft design can lead to some major vibration problems.  In fact, when I contacted a local driveshaft shop to discuss what I needed, one of the guys said that his reference book said to NEVER try and use a 1 piece shaft in place of the stock 2 piece in the Merkur.  Apparently, this is because of the high risk of vibration.  Well, I was determined to replace the fragile looking 2 piece design with a stronger 1 piece driveshaft.  I wanted to use the common 1310 series u-joints, and I told the guy at the shop that I wanted to pursue the 1 piece design.  He said he could do it, but would not offer a warranty.  I told him that was fine, but just to be sure to balance the assembly real good.  I tried to be real careful while setting the driveshaft angle.

The shop was unable to find a flange to match the differential flange, so they made an adapter... more like a small engine flywheel!  As you will see from pictures below, the adapter they made was quite a stout piece.  Unfortunately, it was also quite heavy.  At least I don't have to worry about the adapter failing!  Below is a picture of the custom 1 piece driveshaft.

Custom 1-Piece Driveshaft

Below is a close-up of the C4 slip yoke and also the rear adapter.  If you look closely, you can see some counter bored holes which were supposed to be used to mount the adapter to the differential flange with socket head cap screws.  Unfortunately, they didn't make the counter bores big enough for a standard socket head cap screw.  Even more unfortunate was that Ford used a not so common M8X1.0mm hex bolt for the differential flange.  The extra fine 1.0mm pitch thread made it almost impossible to find a socket head cap screw.  No where I checked had screws with this fine pitch.  I needed some longer screws because the adapter was so thick.  1.25mm and 1.5mm pitch threads in that size were very plentiful, but not the extra fine 1.0mm thread.  I was told by some fastener companies that they should be able to get them, but I would need to buy the entire box since it would be unlikely they could sell the others.  Since I only needed 4, I decided to pass on the idea of ordering a box of 100's or 1000's of these screws!

Drive shaft C4 Slip Yoke and Rear Adapter

Since no matter what fastener I used would require opening up the undersize counter bores on the adapter, I finally decided that I would try to use the stock hex bolts.  Since I don't have free access to the necessary equipment, a friend at work was nice enough to setup the adapter on a mill and use a end mill to sink the larger counter bores needed to be able to allow a socket to fit around the stock hex bolt heads.  The bigger counter bore was also cut deeper to allow the stock length bolts to work.  The resulting holes "broke thru" the sides of the adapter, but that was not a big deal.  The steel adapter still has MORE than enough material to bear the forces transmitted through the drive line.  Besides, the rest of the drive line would be a twisted pretzel long before the adapter ever came close to becoming a weak link.

Driveshaft Adapter with Enlarged Counter bores

The older I've gotten (and now that I have a family), the more conscious I've become of safety issues.  One of the things that I wanted to do was install a drive shaft loop.  The loop acts to constrain the drive shaft in the event either of the u-joints breaks.  In effect, the loop catches the shaft before it is able to hit the ground.  In the case of a front joint breaking at high speeds, it is possible that the drive shaft can dig into the pavement and "pole vault" the car.  This very real risk of flipping a car at high speeds is why drag racers are required to have a drive shaft loop installed.

Since the Merkur XR4Ti come with a center supported 2 piece driveshaft from the factory - and since I wasn't using that center mount with my 1 piece driveshaft - I thought of a simple way to install a driveshaft "loop".  Again, I dug into my bin of scrap materials and found an old piece of 5/8" thick aluminum plate.  I cut and drilled the plate to match up to the old center support mounts.  I got some high strength 12.9 grade socket head cap screws to mount the plate to the car.   A little extra security that hopefully will never be needed.

Driveshaft Safety "Loop"

In order for any automatic transmission to survive, good cooling is required - especially under high performance applications.  I had a couple good size cross flow coolers already sitting around from a previous project, so I just flushed them out with some alcohol and decided to use both.  Even one of these coolers is rated for a much bigger car than the Merkur XR4Ti, but since I already had both I decided to utilize the extra safety margin of running both coolers in series.

Dual High Capacity Transmission Coolers

I used 3/8" diameter transmission cooler hose to plumb in the coolers.  Since my car started life as a 5 speed, I didn't have any of the hard steel lines that an Auto Merkur XR4Ti would have.  The thick walled, high pressure transmission hose was suitable for the task.  While I was plumbing in the coolers, I added a high efficiency in-line filter.  This high quality Magnefine filter has a bypass in the event that it becomes clogged, and also has a magnetic trap to catch any steel particles that might be in the fluid.  I did not feel that the stock transmission screen was up to the task of filtering the transmission fluid.  Besides, at $5/quart, I planned to run the full synthetic Mobil 1 ATF for a long time between fluid changes.  With the in-line filter, it's possible to just replace it with a new filter and just keep running with the same fluid.  The in-line filter is cheap insurance to protect an expensive transmission.

Magnefine In-Line Transmission Filter

The task of filling the C4 transmission was another area that needed to be addressed.  I chose to use a Lokar flexible filler tube.  I ordered the firewall mount version and mounted it to the now vacant battery tray (battery is in the rear hatch area).   The picture below shows the Lokar filler tube/dipstick.  It's a real "diamond in the rough" sitting under the hood of my car.  My car is definitely not pretty to look at - especially under the hood.  I have always focused my limited resources (money & time) to the functional side of things, so the result is not much to brag about in terms of looks!  There's a reason why I often refer to my Merkur XR4Ti as the "Ugly Duckling" when talking with my wife and children.  It's definitely not pretty at first glance, but it does have a lot of hidden potential.

Lokar Ford C4 Firewall Mount Filler Tube

After some real long Saturdays and a LOT of time and effort, the moment of truth was finally approaching.  That final day, I spent around 24+ hours working in the garage in order to be able to lower the car to the ground again.   As I finished up some final details of the Ford C4 transplant, it was the wee hours of the morning.  Realistically (and pessimistically) I fully expected some problems to crop up.  There were so many details involved in this swap - so many areas where something could go wrong.  This write up - as lengthy as it is - only captures some of the behind the scenes work required to make this transmission swap work.  Even if I could do everything perfectly, there were many areas that I had no direct control over (like building of the C4 transmission or balancing the drive shaft).

When I first fired up the car while it was up on jack stands and moved the shift lever thru the various gears, I would not have been surprised to find out that something was wrong.  I was relieved to find that everything appeared to work as it should.  After running it in the air for a while, I crawled under the car to look around for leaks or other signs of problems.  I did find a small drip coming off the side of the transmission.  When I traced it to its source, I found that Accurate Transmission had just forgotten to tighten the test port plug after they did their "hot" dyno test.  A quick tightening with a wrench put an end to that drip.  Then, even more important, I got the car back on the ground and took it for a test drive.  As I drove along, I was very pleased to find that the transmission shifted fine and that all appeared to be well.  I was still concerned that the 1 piece drive shaft could create an ugly vibration problem at higher speeds.  Over the course of the next few days, I was relieved to find that there was not even a hint of vibration - even at high speeds.  In fact, the 1 piece drive shaft was smoother than my old, stock 2 piece drive shaft setup.  As I've said, there were so many areas where things could have gone wrong.  Frankly I was surprised that there weren't any significant "wrinkles to iron out" and I thanked God for this, because as I've said there were many areas where I did not have direct control of the outcome.

After driving it for a couple weeks now, there has been no problems with the transmission transplant.  My Ford C4 transmission shifts firmly and works well.  I've been running with lower turbo boost levels (around 14psi) and trying to give the transmission a gentle start to life.  Not for long though.  Very soon, I plan to turn up the boost to 24psi - back to where it was before the T9 transmission committed Hari-Kari.  "Conveniently", there has been some unrelated driveability problems with the engine that somehow materialized over the past year of the car sitting idle.  These are now almost all worked out and I am beginning to enjoy driving the Merkur again.  Next step is to begin cranking up the turbo boost again.  Finally, I can drive the car without worrying about a weak transmission blowing up...  been there, done that!  Once is enough!

(UPDATE ADDED 08-28-03):  The Ford C4 transmission continues to work just fine.  One thing that has become very clear, very quickly is that a much looser torque converter is really needed.  With a 5 speed and clutch to work with, it was easy to keep the RPM's up and get the turbo into boost quickly.  With the Ford C4 automatic transmission with a very tight torque converter, the car felt like a dog off the line.  A torque converter with a stall of around 3000RPM would probably work well.  Instead of going that route, I decided to just install a nitrous system calibrated with a tiny shot to flash the converter and spool the turbo off the line.  A small 30HP shot makes a HUGE difference and the car behaves more the way it should.  Obviously, if I could do it all again, I'd just try to get a higher stall converter better matched to the off boost low torque of a 4 banger (and not mess with the juice).
     

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